A 1972 agreement between Canada and the United States reduced the amount of phosphates that municipalities had been allowed to dump into the Great Lakes.
这些都是习惯用法啊,为什么要去钻这些呢.英语里名词修饰名词是不多,但不是绝对没有(下次我找给你看,现在想不起来,呵).gmat里一般是避免名词修饰名词的,特别是老长老长的东西.the phosphate amount ,the population change,你觉得看的顺眼吗?对the population change有疑问还可以理解,为什么对the amount of...也要怀疑呢.这个句子请注意后面从句是修饰什么,bc等于是修饰amount了.